Taenia solium: Morphology, Life Cycle and Pathogenesis
Taenia solium is a parasitic organism which belongs to the family Taeniidae under order Cyclophyllidea of class Cestoda. It is also known as the pork tapeworm. It is occurred amongst the pork eaters all over the world. It is the armed tapeworm of human. Adult worm lives in the small intestine (upper jejunum) of human.
Systematic Position
- Phylum: Platyhelminthes
- Class: Cestoda
- Order: Cyclophyllidea
- Family: Taeniidae
- Genus: Taenia
- Species: Taenia solium
Morphology of Taenia solium
Taenia solium has flat, ribbon-like body with white in color. It is triploblastic acoelomate and can grow up to 2 to 3 meters or more in length.
Taenia solium: Image credit-wikimedia commons
The scolex (head) is 1 mm, globular in shape that bears four citcular suckers and a rostellum with a double row of about 30 alternating large and small hooklets.
Scolex of T. solium: Image credit-Wikimedia Commons
Neck is short and after it, the elongated body, known as strobila is present. The entire body is covered by tegument. The strobila is divided into proglottides or segments. These may be 800 to 900 in number (less than 1000). A gravid segment is about 12X6 mm, i.e. longer than broader.
The gravid proglottides contains lots of fertilized eggs which are spherical in shape with 35 to 42 µm in diameter.
Gravid Proglottid of T. solium: Image credit: wikimedia commons
The genital pores are situated marginally and alternate irregularly between right and left margins. The gravid uterus consists of a central main stem with 5 to 10 compound lateral branches on each side. The worm has a life span of about 25 years.
Life Cycle of Taenia solium
Human is the only definitive host. The adult worm is found only in man following eating of undercooked pork containing cysticercus cellulosae larvae.
The adult worms live in the intestine (upper part of jejunum) of man. The gravid proglottid liberates 30,000 to 50,000 eggs before or after leaving the host. Eggs and segments are passed in the stools and contaminate vegetations and water. The eggs are swallowed by pig or human.
Life cycle of T. Solium: Image credit-wikimedia commons
The larvae liberate from the eggs in stomach, penetrate the intestinal mucosa and settle in different parts particularly muscles of pig or human. Here they develop into larva from cysticercus cellulosae. This may also occur due to autoinfection in individuals infected with adult worm.
The egg regurgitates from the intestine into the stomach where it hatches and the larva enters the blood circulation. The adult worm is formed in intestine of human from living larvae ingested with undercooked pork meat.
Pathogenesis and Clinical Features
Adult Worms
Adult worm infection is usually asymptomatic. The diseases are caused by the adult worm, known as taeniasis. If you untreated, the infections with Taenia solium last for about 2–3 years. In many cases, infected people do not show any symptoms up to one year.
The most common intestinal symptoms of taeniasis include:
Cysticercosis
Cysticercus cellulosae larvae are usually found in skeletal muscle and subcutaneous tissues. There may be serious effects due to presence of the larvae in vital organs like brain, eye, etc. The cysticercus may be calcified. Nodules found in subcutaneous tissue. In symptomatic cases, the following symptoms can be expressed:
If the brain is infected by the cysticercus larvae then it is known as neurocysticercosis. It is the leading cause of seizures worldwide. In heavy brain infection especially in children, the following symptoms are expressed:
Diagnosis
Prevention
Treatment
Difference between Taenia solium and Taenia saginata
Characteristic Features | Taenia saginata | Taenia solium |
---|---|---|
Occurrence | Not rare | Rare |
Definitive host | Man | Man |
Intermediate host | Cattle | Man and pig |
Body length | 5-10 meters | 2-3 meters |
Scolex | Large, quadrate. No rostellum or hooks | Small, globular with rostellum and hooks |
Neck | Long | Short |
Proglottides | 1000-2000 | Less than 1000 |
Uterus | Lateral branches, 15 to 30 on each side | Lateral branches, 5 to 10 on each side |
Vagina | Sphincter present | Sphincter absent |
Ovaries | Two, no accessory lobe | Two with an accessory lobe |
Testes | 300 to 400 follicles | 150 to 200 follicles |
Genital pore | Alternate and irregular | Alternate and irregular |
Expulsion of segments | Expelled singly | Expelled in chains of 5 or 6 |
Egg | Spherical in shape | Spherical in shape |